U.S. patent application number 15/114885 was filed with the patent office on 2016-11-24 for control device for continuously variable transmission.
This patent application is currently assigned to JATCO Ltd. The applicant listed for this patent is JATCO LTD, NISSAN MOTOR CO., LTD.. Invention is credited to Tomoaki HONMA, Hiroki IWASA, Masayuki MANNEN, Takaaki MATSUI, Hironori MIYAISHI, Susumu SAITOU, Yuta SUZUKI, Seiichiro TAKAHASHI, Sunghoon WOO, Yoshio YASUI.
Application Number | 20160339921 15/114885 |
Document ID | / |
Family ID | 53777703 |
Filed Date | 2016-11-24 |
United States Patent
Application |
20160339921 |
Kind Code |
A1 |
TAKAHASHI; Seiichiro ; et
al. |
November 24, 2016 |
CONTROL DEVICE FOR CONTINUOUSLY VARIABLE TRANSMISSION
Abstract
Control device for continuously variable transmission has
continuously variable transmission mechanism (CVT) transmitting
power with belt (7) wound around primary and secondary pulley (5,
6); torque convertor (2) having pump impeller (20), turbine runner
(21) and lock-up clutch (2a); and control unit (10) controlling
lock-up clutch (2a) to predetermined engagement state and
controlling the CVT to predetermined transmission ratio, according
to travelling condition. Control unit (10) is configured to, when
shifting lock-up clutch (2a) from disengagement to engagement
state, control transmission ratio of CVT so that when rotation
speed difference (.DELTA.N) between engine speed (Ne) and turbine
speed (Nt) that is rotation speed of turbine runner is
predetermined rotation speed difference (.DELTA.N1) or less,
turbine speed (Nt) approaches engine speed (Ne) more than turbine
speed (Nt1) of case where control of transmission ratio of CVT,
which is set according to travelling condition during shift of
lock-up clutch (2a), is continued.
Inventors: |
TAKAHASHI; Seiichiro;
(Isehara-shi, JP) ; IWASA; Hiroki;
(Sagamihara-shi, JP) ; MIYAISHI; Hironori;
(Sagamihara-shi, JP) ; WOO; Sunghoon; (Atsugi-shi,
JP) ; MATSUI; Takaaki; (Fuji-shi, JP) ; HONMA;
Tomoaki; (Isehara-shi, JP) ; YASUI; Yoshio;
(Fuji-shi, JP) ; SUZUKI; Yuta; (Sagamihara-shi,
JP) ; MANNEN; Masayuki; (Fuji-shi, JP) ;
SAITOU; Susumu; (Moka-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
JATCO LTD
NISSAN MOTOR CO., LTD. |
Fuji-shi
Yokohama-shi |
|
JP
JP |
|
|
Assignee: |
JATCO Ltd
Fuji-shi
JP
NISSAN MOTOR CO., LTD.
Yokohama-shi
JP
|
Family ID: |
53777703 |
Appl. No.: |
15/114885 |
Filed: |
January 7, 2015 |
PCT Filed: |
January 7, 2015 |
PCT NO: |
PCT/JP2015/050204 |
371 Date: |
July 28, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B60W 2710/1005 20130101;
B60W 10/026 20130101; B60W 2710/024 20130101; B60W 30/19 20130101;
B60W 10/107 20130101; B60W 2510/0233 20130101; F16H 61/143
20130101; F16H 61/66259 20130101; B60W 2510/0638 20130101 |
International
Class: |
B60W 30/19 20060101
B60W030/19; B60W 10/107 20060101 B60W010/107; B60W 10/02 20060101
B60W010/02 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 7, 2014 |
JP |
2014-022735 |
Claims
1. A control device for a continuously variable transmission
comprising: a continuously variable transmission mechanism
transmitting power with a belt wound around a primary pulley and a
secondary pulley; a torque convertor provided between an engine and
the continuously variable transmission mechanism, the torque
convertor having a pump impeller rotating integrally with the
engine, a turbine runner rotating integrally with an input shaft of
the continuously variable transmission mechanism and a lock-up
clutch connecting the pump impeller and the turbine runner; and a
control unit controlling the lock-up clutch to a predetermined
engagement state and controlling the continuously variable
transmission mechanism to a predetermined transmission ratio,
according to a travelling condition, and the control unit being
configured to, when shifting the lock-up clutch from a
disengagement state to an engagement state, control a transmission
ratio of the continuously variable transmission mechanism so that
when a rotation speed difference between an engine rotation speed
and a turbine rotation speed that is a rotation speed of the
turbine runner is a predetermined rotation speed difference or
less, the turbine rotation speed approaches the engine rotation
speed more than a turbine rotation speed of a case where control of
a transmission ratio of the continuously variable transmission
mechanism, which is set according to the travelling condition
during the shift of the lock-up clutch, is continued.
2. The control device for the continuously variable transmission as
claimed in claim 1, wherein: the smaller the change speed of the
rotation speed difference is, the greater value the predetermined
rotation speed difference is set to.
Description
[0001] The present invention relates to a control device for a
continuously variable transmission mounted on a vehicle having a
torque converter between an engine and a continuously variable
transmission mechanism.
BACKGROUND ART
[0002] Patent Document 1 discloses a technique of varying a control
gain of a lock-up clutch of a torque converter according to a fluid
temperature when slip-controlling the lock-up clutch.
[0003] However, in a case where the slip-control is affected by
friction characteristics of the clutch, even though the control
gain is varied according to the fluid temperature, it is difficult
to achieve a proper slip-control.
[0004] The present invention was made in view of the above problem.
An object of the present invention is therefore to provide a
control device for the continuously variable transmission which is
capable of achieving a stable engagement of the lock-up clutch.
CITATION LIST
Patent Document
[0005] Patent Document 1: Japanese Unexamined Patent Application
Publication Tokkai-sho 60-143267 (JPS60143267)
SUMMARY OF THE INVENTION
[0006] In order to achieve the above object, a control device for a
continuously variable transmission comprises: a continuously
variable transmission mechanism transmitting power with a belt
wound around a primary pulley and a secondary pulley; a torque
convertor provided between an engine and the continuously variable
transmission mechanism, the torque convertor having a pump impeller
rotating integrally with the engine, a turbine runner rotating
integrally with an input shaft of the continuously variable
transmission mechanism and a lock-up clutch connecting the pump
impeller and the turbine runner; and a control unit controlling the
lock-up clutch to a predetermined engagement state and controlling
the continuously variable transmission mechanism to a predetermined
transmission ratio, according to a travelling condition, and the
control unit is configured to, when shifting the lock-up clutch
from a disengagement state to an engagement state, control a
transmission ratio of the continuously variable transmission
mechanism so that when a rotation speed difference between an
engine rotation speed and a turbine rotation speed that is a
rotation speed of the turbine runner is a predetermined rotation
speed difference or less, the turbine rotation speed approaches the
engine rotation speed more than a turbine rotation speed of a case
where control of a transmission ratio of the continuously variable
transmission mechanism, which is set according to the travelling
condition during the shift of the lock-up clutch, is continued.
[0007] Therefore, since the turbine rotation speed approaches the
engine rotation speed before the lock-up clutch is in a fully
engaged state, torque amplification effect of the torque convertor
can be suppressed at an early stage without excessively lowering
the engine rotation speed when the lock-up clutch is fully engaged.
Further, the lock-up clutch can be shifted from the disengagement
state to the engagement state while lightening an engine load by
suppressing the lowering of the engine rotation speed, and even if
there are variations in coefficient of friction, the lock-up clutch
can be stably fully engaged. It is therefore possible to prevent
odd or awkward feeling associated with change of longitudinal
acceleration from being given to a driver.
BRIEF DESCRIPTION OF DRAWINGS
[0008] FIG. 1 is a system diagram showing a control device of a
continuously variable transmission according to an embodiment
1.
[0009] FIG. 2 is a time chart showing a relationship between a
back-and-forth acceleration (a longitudinal acceleration), an
engine rotation speed and a turbine rotation speed associated with
engagement of a lock-up clutch.
[0010] FIG. 3 is a flow chart showing a lock-up transmission
control operation according to the embodiment 1.
[0011] FIG. 4 is an explanatory drawing showing a detail of the
lock-up transmission control operation according to the embodiment
1.
[0012] FIG. 5 is a predetermined rotation speed difference setting
map according to the embodiment 1.
[0013] FIG. 6 is a turbine rotation speed correction amount setting
map according to the embodiment 1.
[0014] FIG. 7 is a time chart showing a relationship between a
back-and-forth acceleration (a longitudinal acceleration) G, an
engine rotation speed Ne and a turbine rotation speed Nt when
performing the lock-up transmission control operation of the
embodiment 1.
EMBODIMENTS FOR CARRYING OUT THE INVENTION
Embodiment 1
[0015] FIG. 1 is a system diagram showing a control device of a
continuously variable transmission according to an embodiment 1. A
vehicle of the embodiment 1 has an engine 1 that is an internal
combustion engine, a continuously variable transmission and a
belt-type continuously variable transmission mechanism CVT, and a
driving force is transmitted to a driving wheel through a
differential gear. The continuously variable transmission has a
torque convertor 2, an oil pump 3, a forward-reverse switching
mechanism 4 and the belt-type continuously variable transmission
mechanism CVT. The torque convertor 2 has a pump impeller 20
rotating integrally with a driving pawl that is connected to the
engine 1 and drives the oil pump 3, a turbine runner 21 connected
to an input side of the forward-reverse switching mechanism 4 (an
input shaft of the belt-type continuously variable transmission
mechanism CVT) and a lock-up clutch 2a being able to integrally
connect these pump impeller 20 and turbine runner 21. The
forward-reverse switching mechanism 4 is formed from a planetary
gear mechanism and a plurality of clutches 4a, and switches between
forward travel and reverse travel by engagement states of the
clutches 4a. The belt-type continuously variable transmission
mechanism CVT has a primary pulley 5 connected to an output side of
the forward-reverse switching mechanism 4 (an input shaft of the
continuously variable transmission mechanism), a secondary pulley 6
rotating integrally with the driving wheel and a belt 7 wound
around both the primary pulley 5 and the secondary pulley 6 and
transmitting power.
[0016] A control unit 10 reads a range position signal
(hereinafter, respectively called P-range, R-range, N-range and
D-range) from a shift lever 11 that selects a range position by
driver's operation, an accelerator pedal opening signal
(hereinafter, called APO) from an accelerator pedal opening sensor
of an accelerator pedal 12, a primary rotation speed signal Npri
from a primary pulley rotation speed sensor 13 that detects a
rotation speed of the primary pulley 5, a secondary rotation speed
signal Nsec from a secondary pulley rotation speed sensor 14 that
detects a rotation speed of the secondary pulley 6 and an engine
rotation speed Ne from an engine rotation speed sensor 15 that
detects an engine rotation speed. Here, regarding the primary
rotation speed signal Npri, when the range position is D-range, the
primary rotation speed signal Npri is equal to a turbine rotation
speed by engagement of the clutch 4a. Therefore, hereinafter, the
primary rotation speed signal Npri is also described as a turbine
rotation speed Nt.
[0017] The control unit 10 controls an engagement state of the
clutch 4a according to the range position signal. More
specifically, when the range position is P-range or N-range, the
clutch 4a is disengaged. When the range position is R-range, a
reverse clutch (or a brake) is engaged so that the forward-reverse
switching mechanism 4 outputs a reverse rotation. When the range
position is D-range, a forward clutch 4a is engaged so that the
forward-reverse switching mechanism 4 outputs a forward rotation
with the forward-reverse switching mechanism 4 integrally rotating.
Further, the control unit 10 calculates a vehicle speed VSP on the
basis of the secondary rotation speed Nsec. In the control unit 10,
a shift map by which an optimum fuel economy state can be achieved
according to a vehicle travelling condition is set. A target
transmission ratio (corresponding to a predetermined transmission
ratio) is set on the basis of the APO signal and the vehicle speed
VSP according to the shift map. A hydraulic pressure of each pulley
is controlled by feed-forward control on the basis of the target
transmission ratio, and an actual transmission ratio is detected on
the basis of the primary rotation speed signal Npri and the
secondary rotation speed signal Nsec, then the hydraulic pressure
of each pulley is feedback-controlled so that the set target
transmission ratio and the actual transmission ratio become equal
to each other.
[0018] Here, problems occurring upon engagement of the lock-up
clutch 2a in a configuration of the embodiment 1 will be explained.
FIG. 2 is a time chart showing a relationship between a
back-and-forth acceleration (a longitudinal acceleration) G, the
engine rotation speed
[0019] Ne and the turbine rotation speed Nt associated with the
engagement of the lock-up clutch after the vehicle starts.
[0020] At time t1, when a driver depresses the accelerator pedal 12
from a vehicle stop state, the engine rotation speed Ne increases,
and an engine torque is transmitted to the turbine runner 21 with
the engine torque amplified by the torque convertor 2, then the
turbine rotation speed Nt also increases. The vehicle thus
starts.
[0021] At time t2, when the vehicle speed VSP increases and reaches
a predetermined vehicle speed VSP1, an engagement command of the
lock-up clutch 2a is outputted for the purpose of improving fuel
economy. By and with shift of the lock-up clutch 2a from a
disengagement state to an engagement state, a rotation speed
difference .DELTA.N between the engine rotation speed Ne and the
turbine rotation speed Nt gradually becomes smaller. Here, at the
vehicle start, a transmission ratio of the belt-type continuously
variable transmission mechanism CVT is set as a lowest transmission
ratio, and up-shift to High side is gradually done with increase in
the vehicle speed VSP. Therefore, increase in the turbine rotation
speed Nt is more suppressed, as the up-shift is done.
[0022] At time t3, when the rotation speed difference .DELTA.N is
substantially 0 (zero), the engagement of the lock-up clutch 2a is
completed. At this time, if there are variations in a difference
between coefficient of static friction and coefficient of dynamic
friction of friction material of the lock-up clutch 2a, a change
occurs in torque transmitted by the lock-up clutch 2a, and there
arises a problem of causing vibrations (judder) of the
back-and-forth acceleration (the longitudinal acceleration) G of
the vehicle. In particular, the engagement of the lock-up clutch 2a
in a situation in which the increase in the turbine rotation speed
Nt is suppressed by the up-shift of the belt-type continuously
variable transmission mechanism CVT lowers the engine rotation
speed Ne toward the turbine rotation speed Nt, and this causes the
following problems: torque amplification effect of the torque
convertor 2 greatly varies, and because an engine load increases,
amplitude of vibration of the vehicle becomes great.
[0023] Therefore, in the embodiment 1, a lock-up transmission
control operation, which when the lock-up clutch 2a is shifted from
the disengagement state to the engagement state, controls the
transmission ratio of the belt-type continuously variable
transmission mechanism CVT so that the turbine rotation speed Nt
approaches the engine rotation speed Ne more than a case where the
transmission ratio is controlled by a normal transmission ratio
control, is introduced.
[0024] FIG. 3 is a flow chart showing the lock-up transmission
control operation according to the embodiment 1.
[0025] At step S1, on the basis of judgment of a lock-up clutch
engagement control start, a judgment is made as to whether or not
there is an engagement request of the lock-up clutch 2a after the
vehicle start. If YES, the routine proceeds to step S2. If NO, the
present control flow is ended. The lock-up clutch engagement
control starts on the basis of the vehicle speed VSP and the
accelerator pedal opening APO.
[0026] At step S2, a judgment is made as to whether or not the
rotation speed difference .DELTA.N (=Ne-Nt) is a predetermined
rotation speed difference .DELTA.N1 or less. If the rotation speed
difference .DELTA.N is the predetermined rotation speed difference
.DELTA.N1 or less, the routine proceeds to step S3. If NO, the
present step is repeated.
[0027] At step S3, the lock-up transmission control operation is
carried out. Here, since the turbine rotation speed Nt is
determined by a current vehicle speed VSP and a current
transmission ratio, when obtaining a desired turbine rotation speed
Nt, by controlling the belt-type continuously variable transmission
mechanism CVT to a transmission ratio G0 calculated from the
current vehicle speed VSP and the desired turbine rotation speed
Nt, the lock-up transmission control operation is realized. During
execution of the lock-up transmission control operation, when
setting the target transmission ratio, instead of a predetermined
transmission ratio determined from a normal shift map, the
hydraulic pressure of each pulley is controlled with the
transmission ratio GO being the target transmission ratio.
[0028] FIG. 4 is an explanatory drawing showing a detail of the
lock-up transmission control operation according to the embodiment
1. This explanatory drawing shows a relationship between the engine
rotation speed Ne and the turbine rotation speed Nt from a time
period when the engagement command of the lock-up clutch 2a is
outputted to a time period when the lock-up transmission control
operation is ended.
[0029] Phase p1 indicates a timing with which the rotation speed
difference .DELTA.N reaches the predetermined rotation speed
difference .DELTA.N1. This predetermined rotation speed difference
.DELTA.N1 is determined according to a change speed d (.DELTA.N)/dt
of the rotation speed difference .DELTA.N. FIG. 5 is a
predetermined rotation speed difference setting map according to
the embodiment 1. As shown in FIG. 5, the greater the change speed
d (.DELTA.N)/dt is, the smaller value the predetermined rotation
speed difference .DELTA.N1 is set to. When the lock-up clutch 2a is
shifted from the disengagement state to the engagement state, since
the rotation speed difference .DELTA.N changes to a direction in
which the rotation speed difference .DELTA.N becomes smaller, the
change speed d (.DELTA.N)/dt becomes greater as an absolute value
toward a minus side, and a horizontal axis of FIG. 5 has zero at a
right side of FIG. 5.
[0030] That is , when engaging the lock-up clutch 2a and bringing
the rotation speed difference .DELTA.N to 0 (zero) , if the change
of the rotation speed difference .DELTA.N is slow, it takes time to
completely engage the lock-up clutch 2a.
[0031] Therefore, by setting the predetermined rotation speed
difference .DELTA.N1 to be small, a time from the start to the end
of the lock-up transmission control operation is prevented f rom
being too long. Further, when the rotation speed difference
.DELTA.N slowly decreases, also a change speed of decrease of the
engine rotation speed is relatively small. Therefore, even if an
amount by which the transmission ratio of the belt-type
continuously variable transmission mechanism CVT is controlled so
that the turbine rotation speed Nt approaches the engine rotation
speed Ne due to the transmission ratio of the lock-up transmission
control operation is small, it can be said that the great variation
of the torque amplification effect of the torque convertor 2 and
the increase in the engine load are small and the amplitude of
vibration of the vehicle is less apt to be large. On the other
hand, in a case where the rotation speed difference .DELTA.N
rapidly decreases, if the predetermined rotation speed difference
is set to the same predetermined rotation speed difference
.DELTA.N1 as that when the rotation speed difference .DELTA.N
slowly decreases, the time from the start to the end of the lock-up
transmission control operation becomes short. Therefore, by setting
the predetermined rotation speed difference .DELTA.N1 to be larger
than that when the rotation speed difference .DELTA.N slowly
decreases, the time from the start to the end of the lock-up
transmission control operation can be secured. With this setting,
even when the rotation speed difference .DELTA.N rapidly decreases,
the transmission ratio of the belt-type continuously variable
transmission mechanism CVT can be adequately controlled by the
transmission ratio of the lock-up transmission control operation so
that the turbine rotation speed Nt approaches the engine rotation
speed Ne. It is thus possible to reduce the great variation of the
torque amplification effect of the torque convertor 2 and the
increase in the engine load and suppress the amplitude of vibration
of the vehicle.
[0032] In phase p2, after the rotation speed difference .DELTA.N
becomes the predetermined rotation speed difference .DELTA.N1 or
less, a transmission ratio by which the turbine rotation speed Nt
increases at a predetermined increase gradient that is previously
set is set. Here, the predetermined increase gradient is set on the
basis of the accelerator pedal opening APO. FIG. 6 is a turbine
rotation speed correction amount setting map according to the
embodiment 1. Up to a predetermined low opening APO1, the greater
the accelerator pedal opening APO is, the greater value the turbine
rotation speed correction amount Nx is set to, then the
predetermined increase gradient is set to a large increase
gradient. With this setting, as an acceleration demand is stronger,
the lock-up clutch 2a can be fully engaged more quickly, and this
meets driver's acceleration demand. Further, when the accelerator
pedal opening APO is greater than a predetermined opening APO2, the
greater the accelerator pedal opening APO is, the smaller value the
turbine rotation speed correction amount Nx is set to. The reason
of this is because when the accelerator pedal opening APO is
greater than the predetermined opening APO2, an engine torque is
sufficiently outputted, then odd or awkward feeling associated with
an engagement shock is small.
[0033] At the vehicle start, regarding the predetermined
transmission ratio set from the above mentioned shift map, by
gradually up-shifting the transmission ratio from the lowest side
to High side, fuel economy can be improved (see a dotted line in
FIG. 4). The transmission ratio G0 achieving a corrected turbine
rotation speed Nt that is obtained by adding the turbine rotation
speed correction amount Nx to the turbine rotation speed Nt that
corresponds to the predetermined transmission ratio is set.
[0034] By the correction of the turbine rotation speed, for
instance, there are cases where the transmission ratio of the
belt-type continuously variable transmission mechanism CVT is held
at a transmission ratio of the present time (at a relatively low
side transmission ratio) and up-shift to High side is forbidden and
where down-shift toward Low side is done. If the transmission ratio
of the belt-type continuously variable transmission mechanism CVT
is up-shifted in a situation in which the vehicle speed VSP is
increasing, decrease or increase of the turbine rotation speed Nt
is suppressed. In contrast to this, by shifting the transmission
ratio of the belt-type continuously variable transmission mechanism
CVT to the Low side, the turbine rotation speed Nt can also be
increased more quickly with increase in the vehicle speed VSP than
the case where the transmission ratio of the belt-type continuously
variable transmission mechanism CVT is controlled by and at the
predetermined transmission ratio.
[0035] In phase p3, after the rotation speed difference .DELTA.N is
less than a predetermined rotation speed difference .DELTA.N2 and
it is judged that the lock-up clutch 2a is in a state immediately
before the full engagement, rate of change of the rotation speed
difference .DELTA.N is lowered. With this, it is possible to
suppress an inertia shock caused by sudden change of the rotation
speed of the continuously variable transmission mechanism CVT upon
the full engagement. Here, the predetermined rotation speed
difference .DELTA.N2 could be a fixed value. Or alternatively, the
greater the change speed d (.DELTA.N)/dt is, the greater value the
predetermined rotation speed difference .DELTA.N2 is set to. With
this setting, the engagement shock associated with the full
engagement is suppressed.
[0036] In phase p4, after the full engagement is confirmed, the
transmission ratio is controlled so that a current turbine rotation
speed Nt is directed toward a reference turbine rotation speed Nt1
that corresponds to the predetermined transmission ratio determined
by the vehicle speed VSP and the accelerator pedal opening APO of
the present time. At this time, the transmission ratio is
controlled so that rate of change of a difference .DELTA.Nt between
the current turbine rotation speed Nt and the reference turbine
rotation speed Nt1 becomes a predetermined rate of change that is
previously set. With this control, sudden change of the engine
rotation speed Ne and the turbine rotation speed Nt is suppressed,
and a stable acceleration state is achieved.
[0037] FIG. 7 is a time chart showing a relationship between the
back-and-forth acceleration (the longitudinal acceleration) G, the
engine rotation speed Ne and the turbine rotation speed Nt when
performing the lock-up transmission control operation of the
embodiment 1.
[0038] At time t11, when the driver depresses the accelerator pedal
12 from a vehicle stop state, the engine rotation speed Ne
increases, and an engine torque is transmitted to the turbine
runner 21 with the engine torque amplified by the torque convertor
2, then the turbine rotation speed Nt also increases. The vehicle
thus starts.
[0039] At time t12, when the vehicle speed VSP increases and
reaches the predetermined vehicle speed VSP1, an engagement command
of the lock-up clutch 2a is outputted. By and with shift of the
lock-up clutch 2a from the disengagement state to the engagement
state, the rotation speed difference .DELTA.N between the engine
rotation speed Ne and the turbine rotation speed Nt gradually
becomes smaller.
[0040] At time t13, when the rotation speed difference .DELTA.N
becomes the predetermined rotation speed difference .DELTA.N1 or
less, the lock-up transmission control starts, and the turbine
rotation speed Nt increases toward the engine rotation speed Ne. In
other words, in a time period from time t13 to time t14, the
turbine rotation speed Nt approaches the engine rotation speed Ne
at a faster speed than that at which the turbine rotation speed Nt
has approached the engine rotation speed Ne before the time t13.
With this control, the torque amplification effect of the torque
convertor 2 is reduced and the engine load is lightened, then the
lowering of the engine rotation speed Ne is suppressed.
[0041] At time t14, when the lock-up clutch 2a is fully engaged,
after that, the transmission control is done so that the turbine
rotation speed Nt is directed toward the reference turbine rotation
speed Nt1. At time t15, when the turbine rotation speed Nt reaches
the reference turbine rotation speed Nt1, the lock-up transmission
control operation is ended, and the control is shifted to a normal
transmission control.
[0042] By this lock-up transmission control operation, the lock-up
clutch 2a can be smoothly engaged. And even if variations in a
difference between coefficient of static friction and coefficient
of dynamic friction of friction material of the lock-up clutch 2a
exist, it is possible to suppress the change in torque transmitted
by the lock-up clutch 2a and the vibrations of the back-and-forth
acceleration (the longitudinal acceleration) G of the vehicle.
[0043] As explained above, the embodiment can provide the following
operation and effect.
[0044] (1) A control device for a continuously variable
transmission comprises: an engine 1; a continuously variable
transmission mechanism CVT transmitting power with a belt 7 wound
around a primary pulley 5 and a secondary pulley 6; a torque
convertor 2 provided between the engine 1 and the continuously
variable transmission mechanism CVT, the torque convertor 2 having
a pump impeller 20 rotating integrally with the engine 1, a turbine
runner 21 rotating integrally with an input shaft of the
continuously variable transmission mechanism CVT and a lock-up
clutch 2a connecting the pump impeller 20 and the turbine runner
21; and a control unit (control means) 10 controlling the lock-up
clutch 2a to a predetermined engagement state and controlling the
continuously variable transmission mechanism CVT to a predetermined
transmission ratio, according to a travelling condition, and the
control unit 10 is configured to, when shifting the lock-up clutch
2a from a disengagement state to an engagement state, control a
transmission ratio of the continuously variable transmission
mechanism CVT so that when a rotation speed difference .DELTA.N
between an engine rotation speed Ne and a turbine rotation speed Nt
(a rotation speed of the turbine runner 21) is a predetermined
rotation speed difference .DELTA.N1 or less, the turbine rotation
speed (Nt) approaches the engine rotation speed Ne more than a
turbine rotation speed Nt1 of a case where control of a
transmission ratio of the continuously variable transmission
mechanism CVT, which is set according to the travelling condition
during the shift of the lock-up clutch 2a, is continued.
[0045] Therefore, by bringing the turbine rotation speed Nt closer
to the engine rotation speed Ne without excessively lowering the
engine rotation speed Ne, the torque amplification effect of the
torque convertor 2 can be suppressed at an early stage. Further,
the lock-up clutch 2a can be shifted from the disengagement state
to the engagement state while lightening the engine load by
suppressing the lowering of the engine rotation speed Ne, and even
if variations in coefficient of friction exist, the lock-up clutch
2a can be stably fully engaged. It is therefore possible to prevent
the odd or awkward feeling associated with change of the
longitudinal acceleration from being given to the driver. Moreover,
as mentioned above, the transmission ratio G0 achieving the
corrected turbine rotation speed Nt that is obtained by adding the
turbine rotation speed correction amount Nx to the turbine rotation
speed Nt that corresponds to the predetermined transmission ratio
is set. It is thus possible to bring the turbine rotation speed
even closer to the engine rotation speed, as compared with a
turbine rotation speed of a case where the control of the
transmission ratio of the continuously variable transmission
mechanism CVT, which is set on the basis of the travelling
condition during the shift of the lock-up clutch 2a from the
disengagement state to the engagement state, is continued.
Consequently, even in a state in which the transmission ratio is
held, or even in a state of up-shift or down-shift, it is possible
to bring the turbine rotation speed even closer to the engine
rotation speed, as compared with turbine rotation speeds of cases
where the respective controls are continued.
[0046] (2) The smaller the change speed d (.DELTA.N)/dt of the
rotation speed difference .DELTA.N is, the greater value the
predetermined rotation speed difference .DELTA.N1 is set to.
[0047] Therefore, it is possible to suppress a deviation of
rotational angle acceleration between the engine rotation speed Ne
and the turbine rotation speed Nt while shortening a time required
for the full engagement of the lock-up clutch 2a, and stable
engagement of the lock-up clutch 2a can be achieved.
* * * * *